Revert "Limit parallel jobs in CI builds (B2_JOBS=2)"

This reverts commit 9a4f676.

Author: jll63

.github/workflows/ci.yml

@@ -45,8 +45,6 @@ jobs:
       exclude_cxxstd: '98,03,0x,11,14'
       exclude_compiler: gcc-4.9,gcc-5,gcc-6,gcc-7,gcc-8,gcc-9,clang-3.9,clang-4.0,clang-5.0,clang-6.0,clang-7,clang-12
       # temporarily exclude clang-12 because of problem in config-probe
-    env:
-      B2_JOBS: 2
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       COVERITY_SCAN_NOTIFICATION_EMAIL: ${{ secrets.COVERITY_SCAN_NOTIFICATION_EMAIL }}